Butadiene, in order to be useful as a monomer for the production of various polymers such as polybutadiene rubbers and other rubbery polymers, has to be essentially free of vinylacetylene. During the butadiene production, however, vinylacetylene to a certain degree is produced. C.sub.4 -concentrates from naphtha crackers, a major source of crude butadiene, contain a particularly high quantity of vinylacetylene.
In the recovery of butadiene from a mixed C.sub.4 -stream, this C.sub.4 -stream can be prefractionated to remove a portion of the relatively high boiling butene-2's and thereby enrich the butadiene overhead product which is subsequently processed by extractive and fractional distillation to remove butenes and vinylacetylene therefrom. The prefractionation just described can simultaneously reject a minor amount of vinylacetylene. Unfortunately this rejection can, however, not be carried out very far without losing an excessive quantity of butadiene. The final purification of butadiene for reducing the vinylacetylene content to, e.g., less than 50 ppm, is a considerable problem and expensive distillation columns with, e.g., 200 trays have to be used. This problem is aggravated by the fact that vinylacetylene when concentrated in a portion of a fractionator can spontaneously explode and cause large damage.